You're semi-joking, but blockchains could solve this problem cleanly: releasing secret information unless payment is made. In this case, it's a subcase of time-

You're semi-joking, but blockchains could solve this problem cleanly: releasing secret information unless payment is made. In this case, it's a subcase of time-lock crypto (http://www.gwern.net/Self-decrypting%20files http://www.gwern.net/Self-decrypting%20files) and like time-lock crypto in general, can in theory be solved by 'witness encryption'. Witness crypto lets you create an encrypted file whose decryption key is _X_ Bitcoin blocks (specifically, their SHA hashes which are the PoW); after _X_ blocks have been created after a particular block ID, the file can be decrypted. So that's general time-lock crypto, for public broadcast. The witness could be extended to include the transactions: decrypted iff _X_ blocks pass with <_Y_ bitcoins sent to address _Z_. The _Y_ is the loan, and the address _Z_ is the blackmail counterparty. To render the blackmail file permanently undecryptable, one simply sends _Y_ bitcoins to _Z_ before _X_ blocks pass - that is, repaying the loan on time. Who sets up the file? It could be a third party, who only needs to do a one-time setup & broadcast rather than permanently storing keys & needing to be trusted indefinitely. Alternately, you could imagine applying even more crypto magic: homomorphic encryption in which a CNN verifies the presence of nudity and facial recognition with the borrower. (Witness crypto is currently in the 'magic' realm but homomorphic NNs are surprisingly feasible: https://arxiv.org/abs/1412.6181 https://arxiv.org/abs/1412.6181 ). Then the borrower provides the data, the NN runs over it, verifies it is blackmail, the witness crypto-encoded file gets released, and now you have a public secure blackmail system with no trusted third parties. As always, if crypto isn't solving your problems, you aren't using enough of it. :)